I. Field of the Invention
This invention relates to roller cone rock bits with tungsten carbide inserts inserted within insert holes formed within the body of the roller cones.
More particularly this invention relates to the attack angle of each of the tungsten carbide inserts retained within a cone. Each of the inserts have an attack angle with respect to a borehole formation that assures that the insert is primarily in a compressive mode upon initial contact with the formation, and the insert introduces more scraping and shearing to the earthen formation.
II. Description of the Prior Art
Most of the roller cone prior art that teaches the use of tungsten carbide inserts pressed into roller cones have the center line of the tungsten carbide inserts intersecting an axis of the cone. Hence the inserts are generally 90.degree. with respect to a face of the frusto conical cone with the center line of the insert passing through the axial center line of the cone and rock bit journal.
U.S. Pat. No. 3,743,038 teaches an improved drill bit tooth of a milled tooth rotary cone bit having a leading tooth face, i.e. the face first contacting the formation being cut substantially parallel with an axis of rotation of the drill bit cone. The trailing face of the milled tooth is convexly shaped to act as a fulcrum. This tooth configuration allows the tooth to get under and lift a chip from the formation being cut rather than sliding it to the side. The leading face of each of the milled teeth intersects an axial center line of the cone.
The present invention orients each of the tungsten carbide inserts such that the inserts have an attack angle with respect to a formation. The center line of the insert does not intersect the axial center line of each of the cones.
U.S. Pat. No. 3,763,942 teaches a large mechanically driven auger or boring head designed especially for horizontal rock and earth drilling of mines or tunnels. The boring head defines a circular ring of circumferentially spaced tool bits or teeth. The cutting teeth on the ring of the body of the bit project radially outwardly from the peripheral surface of the ring and are tilted forwardly in the direction of rotation of the auger head. The cutting teeth on the body of the bit project forwardly and tilt toward the direction of rotation of the cutting head and are also tilted backwardly to present the tip end of each tooth in a straight forward direction to the surface in which it is cutting. In addition the teeth are staggered so that successive teeth will not have the same cutting track.
The present invention differs in that it is for a rotary cone rock bit wherein each of the tungsten carbide inserts are angled such that they are positioned approximately axially relative to an earthen formation at initial contact. Each of the inserts therefore, are in a more compressive mode rather than in shear as the insert first contacts the bottom of a borehole.
U.S. Pat. No. 4,415,208 is yet another mining bit having individual cutters mounted to a mechanically driven ring for the tunnel cutter. This patent deals with a means of mounting the insert. The cutter bit assembly has an elongated cutter element, a bit holder, a bit block and locking means for removably affixing the bit holder to the bit block. The bit holder has a tapered locking lip and a tapered surface wherein a resulting cutting force provides a locking action against the taper.
This patent, like the foregoing patent, differs from the present invention in that each of the cutter orientation is not in a true compressive mode as the cutter attacks a formation. The present invention describes a roller cone bit wherein the cones roll on a formation bottom with a heavy weight driving the cones into the formation, each of the inserts being angled to assure that the inserts are in a compressive mode upon first contact rather than a shear mode during the cutting operation.
U.S. Pat. No. 4,108,260 describes roller cone rock bits with specially shaped inserts. The insert to the type used for cutter of teeth rock bits used in drilling soft and medium formations of the earth are generally chisel shaped with the flanks converging to a crest. The flanks however of the present invention are asymmetrical with respect to each other. The leading flank is scoop-shaped and the trailing flank is rounded outwardly. The center line of each of the inserts pass through an axial center line of the roller cone.
As stated before, the present invention has each of the center line of the inserts that do not intersect the axial center line of the roller cone, each of the inserts being angled to insure that the insert is primarily in compression upon initial contact with the formation. The foregoing patent, while it describes a scoop-shaped insert, each of the inserts have an orientation that is primarily 90.degree. to a surface of the roller cones, the center line of the asymmetrical inserts intersecting the axial center line of the cone.